1. Field of the Invention
This invention relates generally to integrated circuit (IC) or semiconductor devices. More particularly, the invention pertains to integrated circuit configurations which provide high density modules for mounting on circuit boards and other host apparatus.
2. State of the Art
Integrated circuit semiconductor devices (IC""s) are small electronic circuits formed on the surface of a wafer of semiconductor material such as silicon. The IC""s are fabricated in plurality as part of a wafer. The wafer is then subdivided into discrete IC chips or dice, and then further tested and assembled for customer use through various well-known individual die testing and packaging techniques, including lead frame packaging, Chip-On-Board (COB) packaging, and flip-chip packaging (FCP). Depending upon the die and wafer sizes, each wafer is divided into a few dice or as many as several hundred or more than one thousand discrete dice, each of which becomes an IC package.
the continuing demand for miniaturization has resulted in the development of integrated circuits on dice of very small size. The corresponding miniaturization of external circuitry has not proceeded at the same rate. Thus, there is a need for devices (including the interconnecting circuitry) of increasingly greater density.
Multi-chip modules have typically followed the convention of earlier, single chip packages, in that the reverse sides of bare dice or chips are mounted on a substrate such as a printed circuit board (PCB), leaving the active surface exposed for wire-bonding to the substrate or lead frame. Such is exemplified in U.S. Pat. No. 4,873,615 of Grabbe. Typically, dice are attached to one side only of the substrate, as in U.S. Pat. Nos. 4,992,840, and 4,992,850 of Corbett et al.
Where the device encompasses dice on both sides of the substrate, the reverse sides of the dice are conventionally attached to the substrate, as illustrated in U.S. Pat. No. 5,239,198 of Lin et al.
Stacked groups of packaged devices, often called cubes, have been developed, as exemplified in U.S. Pat. No. 5,016,138 of Woodman, U.S. Pat. No. 5,128,831 of Fox, III et al., U.S. Pat. No. 5,291,061 of Ball, U.S. Pat. No. 5,420,751 of Burns, U.S. Pat. No. 5,455,445 of Kurtz et al., U.S. Pat. No. 5,602,420 Ogata et al., and U.S. Pat. No. 5,637,912 of Cockerill et al. In these references, each non-conductive substrate has one or more IC dies attached to one side only, or when dies are attached to both sides of the substrate, not more than one die is so attached on its active surface. In variants where there is no existing substrate between adjacent dice or packages, the packages have peripheral external leads.
In U.S. Pat. No. 5,291,061 of Ball and U.S. Pat. No. 5,323,060 of Fogal et al., multiple dice are stacked and wire-bonded to circuitry on a substrate which progressively longer wires.
Dice having bond pads, i.e. on the active surface, complicate the construction of multi-chip modules, particularly when wire-bonding is the connection method of choice. As taught in U.S. Pat. No. 5,012,323 of Farnworth, U.S. Pat. Nos. 5,422,435, 5,495,398 and 5,502,289 of Takiar et al., and U.S. Pat. No. 5,600,183 of Gates, Jr., bonding with wire or other conductors necessitates that the stacked dice be of progressively smaller size.
In U.S. Pat. No. 4,996,587 of Hinrichsmeyer et al. and U.S. Pat. No. 5,107,328 of Kinsman, a package is shown with a die within a recess in a carrier. The carrier has shelves which extend over the die, leaving a slot through which the die is wire-bonded to conductive traces on the opposite surface of the shelves. U.S. Pat. No. 5,677,569 of Choi et al. shows a stacked package in which holes in the substrate permit wire-bonding of die pads to the upper surface of the substrate.
In U.S. Pat. No. 5,438,224 of Papagerorge et al. and U.S. Pat. No. 5,477,082 of Buckley, III et al., a pair of dice is shown and attached on its active surfaces to opposite sides of an intermediate layer such as a substrate. In both references, the terminals on the dice are directly coupled to terminals on the same side of the intermediate member by e.g. solder balls. The opposed dice are shown as being coextensive.
In one aspect, the invention comprises a method for forming a high density multi-chip module (MCM) from a plurality of integrated circuit (IC""s) in the form of bare dice with one or more rows of conductive bond pads. The bond pads of each die are preferably formed in a row or rows generally spanning the active surface. The dice are mounted on opposing sides of a substrate in a staggered flip-chip style and wire-bonded through to conductors on the opposite side of the substrate. Metallization in the form of conductive leads on both surfaces of the substrate is thus connected by wire bonds to the dice and to an electrical Input/Output (I/O) means such as a ball-grid array (BGA), edge connector, etc. for connection to an external circuit.
In another aspect, the invention comprises the multi-chip module formed by the method.
In one preferred form, an array of solder balls is formed on one surface of the substrate, in the peripheral area surrounding the die or dice mounted on that surface. Alternatively, a pin-grid array may be used. The multi-chip module may be readily attached by surface mounting on a circuit board, for example.
In another preferred form, an edge connector such as a socket connector as well-known in the art may be used.
The bonded wires within the through-slots in the substrate are preferably surrounded with a xe2x80x9cglob-topxe2x80x9d sealant material following testing. Thus, the wire connections are sealed by glob-top on one side of the substrate and buy the die bonding material on the opposite side of the substrate. A minimum amount of glob-top material is required.
The module construction permits testing of each die after wire-bonding and easy removal and replacement of a defective die, if necessary, without removal of any encapsulant material. The construction is such that the bonded conductive wires are, prior to glob top application, protected from physical damage by their location within through-slots in the substrate and between or adjacent opposing dies. The opportunity for damaging during die testing or die replacement prior to wire encapsulation is greatly reduced.
The module of the invention has a high density, inasmuch as it is formed as an array of bare dice rather than encapsulated packages of greater size. Dice are mounted on both sides of a substrate to form the module, and coplanar dies may be closely spaced, leaving room enough for forming the wire-bonds within the through-slots.
The method of the invention may be employed to surface mount bare dice on e.g. a printed circuit board of an electronic component.